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Leaping Lena

Have a 1994 GMC Sierra 4.3 liter V6. It is galloping and jerking down the raod and sometimes dies at stop lights. Have put in all new tune up parts (it was doing it before I put in the tune up parts). Oh Yea It has a ne w fuel filter too. Any help is appreciated

Possible problems with the fuel injection system. Is it TBI or CPI? At this age, either one can be suspect.

I’m not up on the fuel injection systems , being an old guy , I’m still happy with carburators. But things improve and stuff improves whether some of us can keep up or not. I’m wondering whether it has a faulty EGR valve but don’t know what one looks like on this engine. It also has a oxygen sensor and exhaust sensor somewhere could this be one of it’s problems? If so where are they? I have found Chiltons manuals to be totally worthless and this is the only ones at the local library.

On a GM truck this old, the MAP sensor is a strong suspect. It will cause poor performance like this, but not necessarily set the check engine light. If you do have a check engine light, you should pull the codes and post them here. Do a web search on how to pull OBD1 codes on a GM vehicle and follow the directions. All you need is a paper clip.

To find the EGR & O2 sensors, start with a search for these parts online so you get an idea of what they actually look like. The O2 sensors are threaded into the exhaust pipe. The EGR will be fed by a tube off of the exhaust.

Do the same for a MAP sensor, but you’ll find that attached to the intake manifold someplace.

As mark9207 asked, do you have a check engine light? If so get the codes out & report.

A check of the fuel pressure would be wise.

I’ve heard of the check fuel pressure thought before. How does one do that, with what, and where would i take the reading from in the system?

found the ALDL connection site and got it blinking but it only blinks code 12. There are no tubes comming off the exhaust manifolds except the hot air tube to the air cleaner. As to the egr and 02 sensors, all I can find is sites wanting to sell me a meter for these tests.

On this system, code 12 means the system is in diagnostic mode. Each code will repeat three times, you will have a longer pause, then other codes will follow. If your check engine light is on, there are other codes. If you didn’t wait long enough for the first code to display three times, you need to do this test again. The EGR valve can physically be tested with a vacuum pump or a blunt instrument used with care. If you have a vacuum pump, attach it where the vacuum hose goes and apply vacuum with the engine running. The engine should run noticeably worse. If it doesn’t, the EGR valve is bad. To use a blunt instrument, push up through a slot in the bottom to make the plunger go up in lieu of applying vacuum to do the same thing. You have to be careful not to damage the plunger if you do this. To view data or send commands for this, the O2 sensors, and other such tests, you will need a scan tool such as Snap-On’s MT2500 or Matco’s Determinator. These are prohibitively expensive for a hobbyist or shadetree mechanic (think $3-5k for a used one), so unless you know someone who has one, it’s going to the shop for these tests.